Conventionally, microfabrication by lithography using photoresist compositions has been performed in the production of semiconductor devices. This microfabrication is a fabrication method that includes forming a thin film of a photoresist composition on a substrate to be fabricated such as a silicon wafer, radiating active rays such as ultraviolet rays onto the thin film via a mask pattern in which a pattern of a semiconductor device is formed, developing the film, and etching the substrate to be fabricated such as a silicon wafer using the obtained photoresist pattern as a protective film. In recent years, higher integration of semiconductor devices has been pursued, and there is a trend for the active rays used to have shorter wavelengths from KrF excimer lasers (248 nm) to ArF excimer lasers (193 nm). This trend has been accompanied by significant disadvantages of effects due to standing waves and diffuse reflection of the active rays from the substrate. Accordingly, methods have been extensively studied that include providing an anti-reflective coating (Bottom Anti-Reflective Coating, BARC) between the photoresist and the substrate to be fabricated.
When a finer resist pattern is further pursued, an issue of resolution and a defective condition in which the resist pattern collapses after development may occur, and thus thinner resists is required. This makes it difficult to achieve sufficient resist pattern film thickness for fabrication of a substrate, and thus a process has become necessary in which the function of a mask during the substrate fabrication is imparted not only to the resist pattern, but also to a resist underlayer film that is formed between the resist and a semiconductor substrate to be fabricated. As a resist underlayer film for such a process, unlike a conventional resist underlayer film having a high etching-rate property (high etching rate), a resist underlayer film for lithography having a selection ratio of dry etching rate to the dry etching rate of the resist that is close to 1, a resist underlayer film for lithography having a smaller selection ratio of dry etching rate to the dry etching rate of the resist, or a resist underlayer film for lithography having a smaller selection ratio of dry etching rate to the dry etching rate of the semiconductor substrate is required.
Example of a polymer for the resist underlayer films include the following.
Resist underlayer film-forming compositions in which a carbazole novolak resin is used are exemplified (see Patent Document 1).
While such a finer resist pattern is being pursued, a three-layer process is widely used for forming a silicon-containing resist intermediate layer film and a resist underlayer film in the lower layer of the resist. There is a demand for using the intermediate layer film the film thickness of which is equal to or smaller than 50 nm from the viewpoint of pattern collapse and etching fabrication accuracy. When the film thickness of the silicon-containing intermediate layer film is equal to or smaller than 50 nm, the anti-reflection effect of the silicon-containing intermediate layer film decreases, and thus the resist underlayer film is required to have an n value and a k value that are appropriate. More specifically, an underlayer film that has a high n value, a low k value, transparency, and also high etching resistance is required.
Examples of a polymer for the resist underlayer film having an n value and a k value that are appropriate include the following.
Resist underlayer film-forming compositions in which a polymer containing a product obtained by reaction of naphthol with dicyclopentadiene is used are exemplified (see Patent Document 2).